1. Field of the Invention
The present invention relates to lubricating oil compositions comprising a base oil selected from the group consisting of mineral oils, synthetic oils and mixtures thereof boiling in the lubricating oil boiling range and additives which neutralize the prooxidants which cause the oxidative decomposition of the lubricating oil composition.
2. Description of the Related Art
Currently, lubricating oil formulations are rendered resistant to oxidative degradation by the addition to the lubricating oil formulations of free radical scavenger antioxidants such as sterically hindered phenols, hindered amines and mixture thereof and hydroperoxide decomposers such as zinc dialkyldithiophosphate.
Most of such antioxidants as are presently used are consumed by the oxidation promoters in the oil (the prooxidants) on a stoichiometric basis. Antioxidants can be added to lubricating oil formulations only in limited quantities and consequently even if and when the maximum practical amount is added they are quickly consumed and disappear, with the undefended oil rapidly oxidizing with their disappearance.
Other antioxidants such as copper acetylacetonates, while consuming the prooxidants on a more than stoichiometric basis are still themselves used-up at a rate of less than about 10:1 and therefore, while superior to the phenolic and aminic antioxidants are still not sufficiently long lived or suitable for the next generation of extended drain lube oils or sealed for life/filled for life lubricant environments.
Prooxidants are continuously generated in the lubricant during routine use or added/introduced into the oil by blow-by gases, or exhaust gas recirculation as during the operation of internal combustion engines.
U.S. Pat. No. 4,705,641 teaches the combination of copper and molybdenum salts as being an effective antioxidant and antiwear additive for hydrocarbons such as lube oils. The total concentration of copper salt and molybdenum salt is such that the concentration of metal or metal ion may range from about 0.006 wt % to about 0.5 wt %, preferably from about 0.009 wt % to about 0.1 wt % of the basestock. The concentration of the copper salt may range between about 0.002 wt % and about 0.3 wt % while the concentration of the molybdenum salt ranges between about 0.004 wt % and about 0.3 wt %. The copper salt preferably is selected from the group of carboxylates consisting of oleates, stearates, naphthenates and mixtures thereof. The molybdenum salt preferably is selected from the group of carboxylates consisting of naphthenates, oleates, stearates and mixtures thereof.
U.S. Pat. No. 4,122,033 discloses an oxidation inhibitor and a method for using the oxidation inhibitor for hydrocarbon materials, particularly lube oils. This patent discloses that one or more transition metal containing compounds can be utilized in combination with one or more peroxide decomposer compounds selected from aliphatic amines, alkyl selenides, alkyl phosphines and phosphates wherein the aliphatic and alkyl portions of said compound each contain from about 1 to about 50 carbon atoms as oxidation inhibitors in organic compositions subject to auto-oxidation. Among the transition metal compounds useful according to the patent are the salts of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, yttrium, zirconium, niobium, molybdenum, tellurium, ruthenium, rhodium, palladium, and silver, to mention a few. This patent further states, at column 8, that when a combination of metals is used a synergistic effect will be noted if the sum of electromotive force voltages favors the presence of the stronger inhibitor and/or the weaker catalyst and is, generally, positive. Additionally, the combination will be effective as a corrosion inhibitor at concentrations of about 100 ppm by weight, or less, when the amount of peroxide decomposer complexing agents or the like approaches 20,000 ppm by weight. In effect the effectiveness of the transition metal compounds is dependent upon relatively high concentrations of the peroxide decomposer compounds.
U.S. Pat. No. 2,398,414 teaches organic selenium compounds and organic tellurium compounds of the formula:R—(X)m—R1 wherein R and R1 are like or unlike radicals of alkyl structure at least one of which contains not less than 8 carbon atoms, X is selenium or tellurium and m is 1 or 2. These organic compounds are useful as mineral oil additives and are also useful as antioxidants for vegetable oils, rubber and other organic materials which are subject to oxidative deterioration. The “alkyl” radicals can be straight or branched chain in nature as well as being saturated or unsaturated and can also be cycloalkyl or cycloaliphatic. They can be substituted by aromatic groups such as phenyl, hydroxyphenyl and aminophenyl groups. Polar groups such as chloro-, bromo-, hydroxyl-, ether, keto, amine, free carboxyl, metallo carboxyl, carboxy ester, mercapto, mercaptide, mono-, di- and polysulfide, etc., may also be substituted in the R and R1 groups. See also U.S. Pat. No. 2,543,074 and U.S. Pat. No. 2,577,719.
U.S. Pat. No. 4,867,890 teaches oil soluble organo copper compounds as antioxidants. The copper may be in the μ cuprous or cupric form. The copper may be in the form of the copper dihydrocarbyl thio- or di-thio-phosphates wherein copper may be substitute for zinc in such compounds. The copper may also be in the form of the copper salt of a synthetic or natural carboxylic acid, e.g., C10-C18 fatty acids such as stearic or palmitic, but the unsaturated acids such as oleic or the branched carboxylic acids such as naphthenic acids of molecular weight from 200 to 500 or the synthetic acids are preferred. Oil-soluble copper dithiocarbamate as well as copper sulfonates, phenates, and acetylacetonates may also be used. The copper compound is employed in an amount sufficient to contribute 5 to 500 ppm copper to the oil.
U.S. Pat. No. 5,650,381 teaches a lubricating oil composition which contains from about 100 to 400 ppm of molybdenum from a molybdenum compound which is substantially free of active sulfur and about 750 to 5,000 ppm of a secondary diaryl amine. The combination of ingredients is reported as providing the lubricating oil with improved oxidation control and friction modifier performance. Oil soluble molybdenum compounds include those prepared from a molybdenum source such as ammonium molybdenates, alkali and alkaline earth metal molybdeates, molybdenum trioxide and molybdenum acetyl-acetonates and an active hydrogen compound such as alcohols and polyols, primary and secondary amines and polyamines, phenols, ketones, anilines, etc.
Molybdenum salts such as the carboxylates, e.g., molybdenum naphthenate, are a preferred group of molybdenum compounds.
U.S. Pat. No. 6,121,211 teaches a lubricating oil composition comprising a major amount of a base oil of lubricating viscosity and a minor amount of at least one thiocarbamate and a sludge preventing and seal protecting amount of at least one aldehyde or epoxide or mixture thereof. The thiocarbamates include those of the formula:
wherein R1 and R2 are independently alkyl of 1 to about 7 carbon atoms, aryl, aralkyl or together form an alicylic or heterocyclic ring in which the ring is completed through the nitrogen and wherein when n is 2, T is a divalent metal. Suitable relevant metals include alkaline earth metals, cadmium, magnesium, ten, molybdenum, iron, copper, nickel, cobalt, chromium and lead. Specific examples include cadmium dibutyldithiocarbamate, cadmium, dioctyl dithiocarbamate, cadmium octylbutyl-di-thiocarbamate, magnesium dibutyl dithiocarbamate, magnesium dioctyl dithio-carbamate, cadmium dicetyldithio carbamate. The patent contained no examples in which a divalent metal dialkyl dithiocarbamate was added to oil either alone or in combination with the aldehyde or epoxide.
JP 53024957 teaches the liquid phase oxidation of cyclohexane into cyclohexanol by oxidizing the cyclohexane with an oxygen containing gas in the liquid phase in the presence of metal salts selected from the group consisting of Cr, V and W of an organic acid or a chelate compound as a catalyst. In the process the cyclohexane is first converted into cyclohexyl hydroperoxide which is then rapidly decomposed into cyclohexanol and cyclohexanone. Examples of catalyst include chromium, vanadium and tungsten naphthenates and chromium acetylacetonate. The amount of the catalyst is preferably 0.1 to 20 ppm more preferably 0.5-10 ppm of the metal atom based on the cyclohexane.
U.S. Pat. No. 4,766,228 teaches a metal dihydrocarbyldithiophosphoryl dithio-phosphate material of the formula
wherein R is a monovalent substantially hydrocarbon-containing radical of 1-30 carbons, x and y are each H or a monovalent substantially hydrocarbon containing radical of 1 to 30 carbons, M is a metal selected from zinc, cadmium, lead and antimony or an oxygen and/or sulfur-containing molybdenum complex and n is the valence of the metal. This material is useful as a lubricant additive (see also U.S. Pat. No. 4,882,446).
U.S. Pat. No. 5,439,604 teaches compositions containing metal salts, preferably copper or zinc salts, of polyalkenyl substituted monounsaturated mono- or dicarboxylic acids which may be used as a compatibilizing material for mixtures of dispersants, detergents, anti-wear and antioxidant materials. The antioxidant can be a copper antioxidant and include copper salts of C10-C13 fatty acid, copper salt of naphthenic acid, copper dithiocarbamate, copper sulfonate, copper phenate or copper acetylacetonate.
U.S. Pat. No. 5,631,212 teaches an engine oil of improved wear resistance and antioxidancy comprising base oil, an oil soluble copper salt, an oil soluble molybdenum salt, a Group II metal salicylate and a borated polyalkenyl succinimide. Molybdenum salts are the oil soluble salts of synthetic or natural organic acids, preferably C4 to C30 saturated and unsaturated fatty acids, e.g., molynaphthanate, molyhexanate, molyoleate, molyxanthate and molytallate.
U.S. Pat. No. 4,066,561 teaches organometallic complexes of the formula:
wherein, as defined in the patent                n is an integer of from 1 to about 10, preferably from 1 to about 5;        A is an aromatic moiety, preferably phenyl or naphthyl;        M is a polyvalent metal, such as, for example, Be, Mg, Ca, Ba, Mn, Co, Ni, Pd, Cu, Zn and Cd;        X is a radical selected from the group consisting of organophosphoro, organocarboxyl, organoamino, organosulfonyl, organothio, organooxy, nitrate, nitrite, phosphate, sulfate, sulfonate, oxide, hydroxide, carbonate, sulfite, fluoride, chloride, bromide and iodide;        R1 and R2 are alkyl of from 1 to about 10 carbon atoms, aryl, hydrogen,        
                 or a combination thereof;        R′ is alkyl of from 1 to about 10 carbon atoms, aryl or hydrogen;        R3, R4, R5 and R6 are hydrogen, alkyl of from 1 to about 200 carbon atoms, aryl, alkyl-substituted aryl where the alkyl substituent is comprised of form 1 to about 200 carbon amounts, carboxyaryl, carbonylaryl, aminoaryl, mercaptoaryl, halogenoaryl or combinations thereof.        
The metal complexes reportedly stabilize the lubricant to which they are added against oxidation.
U.S. Pat. No. 5,824,627 teaches a lube oil composition containing a major to amount of a lube base oil and a minor amount of an additive having the formula M4-yMoyS4LnQz and mixtures thereof, wherein M is a metal selected from Cr, Mn, Fe, Co, Ni, Cu, and W, L is independently selected organic groups selected from dithiophosphates, thioxanthates, phosphates, dithiocarbamates, thio-phosphates and xanthates, having a sufficient number of carbon atoms to render the additive soluble or dispersible in the oil, and Q is a neutral electron donating compound, y is 1 to 3, n is 2 to 6, and z is zero to 4, and the L provide a total charge sufficient to neutralize the charge on the M4-yMoyS4 core. Thiocubane cores are preferred and these typically have the formula M4-yMoyS4LnQz, wherein y is 1 to 3, n is 2 to 6 and z is 0 to 4.
U.S. Pat. No. 3,707,498 teaches antioxidant additives comprising a mixture of a metal dialkyldithiocarbamate and a tertiaryalkyl primary amine. The metal is from Group IIb, IVa and Va and preferably are zinc cadmium, lead and antimony.
U.S. Pat. No. 3,649,660 teaches silyl ocenes as being useful antioxidants for organopolysiloxane fluids. The silylorganometallocenes are selected from the class of    (a) polymers of the formula
    (b) copolymers having units of the formula
and at least one unit of (a), and    (c) disiloxanes of the formula
where R is a monovalent hydrocarbon radical, R″ is a divalent hydrocarbon radical, and (C5Q4)M(C5Q5) is an organometallocene, where Q is selected from hydrogen, an electron donating organic radical, and an electron withdrawing organic radical and M is a transition metal, a is a whole number equal from 0 to 2 and b is a whole number equal from 0 to 3.
In U.S. Pat. No. 3,649,600 Transition metal is defined to include all metals of Group III to VIII of the Periodic Table capable of forming a π complex with a cyclopentadienyl radical to form a metallocene. The transition metals that are operative in the present invention are, for example, metals having atomic numbers 22 to 28, 40 to 46, and 71 to 78, such as titanium, vanadium, chromium, manganese, iron, cobalt, nickel, zirconium, columbium, molybdenum, technetium, ruthenium, rhodium, palladium, hafnium, tantalum, tungsten, rhenium, osmium, iridium and platinum (see also U.S. Pat. No. 3,745,129).
U.S. Pat. No. 3,351,647 teaches a composition of the general formula:
wherein R is a substantially hydrocarbon radical; M is a metal selected from the group consisting of zinc, calcium, copper, nickel, cobalt, chromium, lead, and cadmium; A, B and C are radicals selected from the class consisting of hydrogen and substantially hydrocarbon radicals; x is the valence of M; y is from about 0.5 to about 6.
The compositions are useful as oil additives and function is antioxidant and antiwear agents.
U.S. Pat. No. 4,427,560 teaches a formulation containing among other additives an oxidation inhibitor.
The oxidation inhibitors or antioxidants have high enough molecular weights to ensure that they remain stable in a hot crankcase oil, e.g., 300° F. and, in addition, enhance the corrosion preventive properties of the copper and lead corrosion inhibitors also present in the formulation by interrupting or terminating the attack of oxidants upon copper/lead-bearing metal. One type of corrosion is an oxidative process involving the loss of electrons from the corroding metal by an oxidant such as oxygen, air, nitrogen oxides, partially burned gasoline, blow-by products and the like. The oxidation inhibitors comprising sulfur bridge, bis hindered phenols effectively limit or prevent the attack of oxidants on copper/lead metal.
The bis(dithiobenzyl) metal derivatives preferably have the formula:

U.S. Pat. No. 5,015,402 teaches basic metal and multi-metal dihydrocarbyl-phosphorodithioates and phosphoromonothioates as antioxidant additives. These materials are represented by the general formula:[Z]d[RO)2PSS]yMaXb  (I)wherein M and X represent different metal cations selected from the group consisting of zinc, copper, chromium, iron, copper, manganese, calcium, barium, lead, antimony, tin and aluminum; Z is an anion selected from oxygen, hydroxide and carbonate; R is independently a linear or branched alkyl group of 1 to about 200 carbon atoms, or a substituted or unsubstituted aryl group of 6 to about 50 carbon atoms; a and b are integers of at least one and are dependent upon the respective oxidation states of M and X; y is a whole integer which is dependent upon the oxidation states of M and X; and d is an integer of 1 or 2.
U.S. Pat. No. 3,764,534 teaches a composition comprising a lubricating oil and at least one thioorganometallic complex of the formula:
in which M is selected from the transition metals and zinc, cadmium, tin, lead, antimony and bismuth; n is the oxidation degree of M, R1 and R2 are each a monovalent hydrocarbon radical having one to 20 carbon atoms and 0 to 3 heteroatoms selected from the group consisting of halogen, oxygen, sulfur and nitrogen; Y is selected from the hydrogen atom and the radicals R′, R′O, R′S and R′CO in which R′ is a hydrocarbon radical of 1 to 20 carbon atoms; Y and R1 or R2 may form a divalent hydrocarbon radical containing 1 to 20 carbon atoms and 0-3 heteroatoms selected form oxygen, sulfur and nitrogen; and each atom Z is oxygen or sulfur, at least one of the 2n atoms Z being sulfur.
It is recited that these materials exhibit high antioxidancy activity even at high temperature. They can be used with base oils of petroleum origin as well as with synthetic base oils. See also GB 1,322,699.
GB 1,358,961 teaches that 9,10-dihydroanthracene acts synergistically with certain metal β-diketone complexes to provide antioxidancy. The metal β-diketone complexes are of the formulaM(-O—CR1═CR2—CR3═O)n wherein M is a metal, n is 2 or 3, R2 is hydrogen or an alkyl group having 1 to 20 carbon atoms and R1 and R3 are alkyl, aryl or alkoxy groups having 1-10 carbons.
U.S. Pat. No. 4,849,123 teaches drivetrain fluids comprising oil soluble transition metal compounds which address low temperature thickening of ATF's and high temperature thickening or gear oils. The oil soluble transition metal compound is a branched chain oil-soluble transition metal salt with the proviso that the transition metal is not zinc, wherein said transition metal salt is a salt wherein the non-metal moiety is selected from dihydrocarbylthio- or dithiophosphate, a dihydrocarbylthio- or dithiocarbamate, or mixtures thereof and wherein the metal is selected from copper, cobalt, tungsten, titanium, manganese, iron, chromium, nickel, vanadium, molybdenum or mixtures thereof.
As a consequence of more stringent and demanding performance requirements on lubricating oils, for example fill for life oils, sealed bearings oils and greases, or modern extended drain engine lubricating oils to perform better, for longer periods and under more severe conditions of temperature and load over longer times as manifested by current and future lubricating oil specifications, particularly engine oil classifications for diesel lubricants (PC7 and PC8) and passenger car lubricants (GF-3 and GF-4), more efficient, longer lasting and more robust antioxidants are required for use in the lubricants.